U.S. patent number 9,682,900 [Application Number 14/543,405] was granted by the patent office on 2017-06-20 for hydrocarbon conversion.
This patent grant is currently assigned to ExxonMobil Chemical Patents Inc.. The grantee listed for this patent is ExxonMobil Chemical Patents Inc.. Invention is credited to Guang Cao, Juan D. Henao, Paul F. Keusenkothen, Abhimanyu O. Patil.
United States Patent |
9,682,900 |
Keusenkothen , et
al. |
June 20, 2017 |
Hydrocarbon conversion
Abstract
This disclosure relates to the conversion of methane to higher
molecular weight (C.sub.5+) hydrocarbon, including aromatic
hydrocarbon, to materials and equipment useful in such conversion,
and to the use of such conversion for, e.g., natural gas
upgrading.
Inventors: |
Keusenkothen; Paul F. (Houston,
TX), Henao; Juan D. (Houston, TX), Patil; Abhimanyu
O. (Westfield, NJ), Cao; Guang (Princeton, NJ) |
Applicant: |
Name |
City |
State |
Country |
Type |
ExxonMobil Chemical Patents Inc. |
Baytown |
TX |
US |
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Assignee: |
ExxonMobil Chemical Patents
Inc. (Baytown, TX)
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Family
ID: |
52011320 |
Appl.
No.: |
14/543,405 |
Filed: |
November 17, 2014 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20150158792 A1 |
Jun 11, 2015 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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61912901 |
Dec 6, 2013 |
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Foreign Application Priority Data
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Feb 5, 2014 [EP] |
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14153945 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C07C
2/864 (20130101); C07C 2/76 (20130101); C07C
2/865 (20130101); C07C 2/76 (20130101); C07C
15/00 (20130101); C07C 2529/06 (20130101); C07C
2529/40 (20130101); C07C 2529/44 (20130101); C07C
2529/46 (20130101); C07C 2529/87 (20130101); Y02P
30/20 (20151101); C07C 2529/48 (20130101) |
Current International
Class: |
C07C
2/76 (20060101); C07C 2/86 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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101244969 |
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Aug 2008 |
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CN |
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0293032 |
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Jul 1993 |
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EP |
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1704132 |
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Jul 2005 |
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EP |
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2184269 |
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May 2010 |
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EP |
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2191212 |
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Dec 1987 |
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GB |
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97/17290 |
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May 1997 |
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WO |
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2004/087624 |
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Oct 2004 |
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WO |
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2012/099674 |
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Jul 2012 |
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WO |
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|
Primary Examiner: Bullock; In Suk
Assistant Examiner: Louie; Philip
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims priority to U.S. Ser. No. 61/912,901, filed
Dec. 6, 2013, the disclosure of which is incorporated herein by
reference in its entirety. This application also claims priority to
EP 14153945.2, filed Feb. 5, 2014. Cross reference is made to the
following related patent applications: (i) P.C.T. Patent
Application No. PCT/US2014/065947, filed Nov. 17, 2014; (ii) U.S.
patent application Ser. No. 14/543,271, filed Nov. 17, 2014; (iii)
P.C.T. Patent Application No. PCT/US2014/065961, filed Nov. 17,
2014; (iv) U.S. patent application Ser. No. 14/543,243, filed Nov.
17, 2014; (v) P.C.T. Patent Application No. PCT/US2014/065969,
filed Nov. 17, 2014; (vi) U.S. patent application Ser. No.
14/543,426, filed Nov. 17, 2014; (vii) P.C.T. Patent Application
No. PCT/US2014/065956, filed Nov. 17, 2014; and (viii) U.S. patent
application Ser. No. 14/543,365, filed Nov. 17, 2014.
Claims
The invention claimed is:
1. A process for producing C.sub.5+ hydrocarbon, the process
comprising: (a) providing a feed comprising a C.sub.1+ inorganic
oxygenate and .gtoreq.9 mole % of methane, per mole of feed,
wherein a molar ratio of methane to C.sub.1+ inorganic oxygenate is
in a range of 0.6:1 to 20:1, and wherein the C.sub.1+ inorganic
oxygenate comprises aldehyde; (b) contacting the feed with a
catalyst comprising at least one molecular sieve and at least one
dehydrogenation component under conditions, including a temperature
less than 700.degree. C., effective to convert at least a portion
of the methane and at least a portion of the aldehyde in the feed
to a product comprising at least 5 wt. % of C.sub.5+ hydrocarbons
based on the weight of the product, wherein the C.sub.5+
hydrocarbons comprise C.sub.6 to C.sub.10 aromatics; and (c)
separating at least part of the C.sub.5+ hydrocarbons from the
product.
2. The process of claim 1, wherein the molar ratio of methane to
C.sub.1+ inorganic oxygenate in the feed is in the range of from
5:1 to 15:1.
3. The process of claim 1, wherein the C.sub.1+ inorganic oxygenate
further comprises CO added to the feed as syngas, and wherein the
syngas has a molecular hydrogen to CO molar ratio .ltoreq.4.
4. The process of claim 3, wherein at least a portion of the syngas
is produced by partial oxidation of methane.
5. The process of claim 1, wherein the temperature is less than
600.degree. C., and the feed further comprises C.sub.2+ aliphatic
hydrocarbons and/or molecular hydrogen, and wherein the C.sub.2+
aliphatic hydrocarbons comprise one or more C.sub.2 to C.sub.5
alkanes.
6. The process of claim 5, wherein the feed further comprises
C.sub.1+ organic oxygenates, and wherein the C.sub.1+ organic
oxygenates comprise C.sub.1 to C.sub.4 organic oxygenates.
7. The process of claim 1, wherein the feed comprises .gtoreq.25
mole % of methane.
8. The process of claim 1, wherein (i) the molecular sieve
comprises an aluminosilicate and/or a gallosilicate, and wherein
the molecular sieve has an average pore size of 5.4 .ANG. to 7
.ANG., and (ii) the dehydrogenation component comprises a metal or
compound thereof from Groups 3 to 13 of the Periodic Table.
9. The process of claim 1, wherein the temperature of step (b) is
.ltoreq.300.degree. C., and the contacting conditions of step (b)
further comprises a pressure in the range of from 1.2 bar
(absolute) to 4 bar (absolute) and/or a feed gas hourly space
velocity of .gtoreq.100 cm.sup.3/h/g of catalyst.
10. The process of claim 1, wherein (i) the product comprises,
.ltoreq.10.0 wt. % C.sub.2 to C.sub.4 hydrocarbons, based on the
weight of the product, (ii) methane conversion is .gtoreq.5.0 wt.
%, based on the weight of methane in the feed, and (iii) the
C.sub.5+ hydrocarbons comprise .gtoreq.90.0 wt. % of C.sub.6 to
C.sub.10 aromatics, based on the weight of the C.sub.5+
hydrocarbons.
Description
FIELD
This disclosure relates to the conversion of methane to higher
molecular weight (C.sub.5+) hydrocarbon, including aromatic
hydrocarbon, to materials and equipment useful in such conversion,
and to the use of such conversion for, e.g., natural gas
upgrading.
BACKGROUND
Although methane is abundant, its relative inertness has limited
its utility in conversion processes for producing higher-value
hydrocarbon. For example, oxidative coupling methods generally
involve highly exothermic and potentially hazardous methane
combustion reactions, frequently require expensive oxygen
generation facilities, and produce large quantities of
environmentally sensitive carbon oxides. In addition, non-oxidative
methane aromatization is equilibrium-limited, and temperatures
.gtoreq.about 800.degree. C. are needed for methane conversions
greater than a few percent.
To obviate this problem, catalytic processes have been proposed for
co-converting methane and one or more co-reactants to higher
hydrocarbon, such as aromatics. For example, U.S. Pat. No.
5,936,135 discloses reacting methane at a temperature in the range
of 300.degree. C. to 600.degree. C. with (i) a C.sub.2-10 olefin
and/or (ii) a C.sub.2-10 paraffin in the presence of a bifunctional
pentasil zeolite catalyst, having strong dehydrogenation and acid
sites, to produce aromatics. The preferred mole ratio of olefin
and/or higher paraffin to methane and/or ethane in the feed ranges
from about 0.2 to about 2.0.
Other processes utilize organic oxygenate as a co-reactant for the
non-oxidative methane conversion to produce higher hydrocarbon,
including aromatics. For example, U.S. Pat. No. 7,022,888 discloses
a process for the non-oxidative conversion of methane
simultaneously with the conversion of an organic oxygenate,
represented by a general formula: CnH.sub.2n+1OCmH.sub.2m+1,
wherein C, H and O are carbon, hydrogen and oxygen, respectively; n
is an integer having a value between 1 and 4; and m is an integer
having a value between zero and 4. The methane and oxygenate are
converted to C.sub.2+ hydrocarbon, particularly to gasoline range
C.sub.6-C.sub.10 hydrocarbon and hydrogen, using a bifunctional
pentasil zeolite catalyst, having strong acid and dehydrogenation
functions, at a temperature below 700.degree. C.
However, since the co-reactants employed in the processes of the
'135 and '888 patents are themselves valuable commodities, there is
interest in developing alternative routes for the conversion of
methane into aromatics and particularly routes that allow more
methane to be incorporated into the aromatic product, and that
operates over a broad molar ratio range of methane to co-reactant
in the feed.
SUMMARY
It has been found that methane can be more efficiently converted to
C.sub.5+ hydrocarbon when the conversion is carried out in the
presence of organic oxygenate and C.sub.2+ aliphatic hydrocarbon.
It is observed that including C.sub.2+ aliphatic hydrocarbon with
the methane and organic oxygenate results in a surprising increase
in the yield of C.sub.5+ hydrocarbon from the conversion. While not
wishing to be bound by any theory or model, it is believed that the
reaction is more efficient than prior art processes, which do not
utilize a C.sub.2+ aliphatic hydrocarbon co-reactant with the
organic oxygenate, because the C.sub.2+ aliphatic hydrocarbon
assists the cyclization of methane fragments during the conversion
reaction. Moreover, the reaction can be carried out efficiently at
relatively low temperatures, e.g., .ltoreq.700.degree. C., such as
.ltoreq.300.degree. C., over a broad range of methane to organic
oxygenate molar ratio, e.g., in the range of from 0.6:1 to
20:1.
These findings have led to the development of processes for
converting to C.sub.5+ hydrocarbon a feed comprising C.sub.2+
aliphatic hydrocarbon, C.sub.1+ organic oxygenate, and at least 9
mole % of methane, the mole % being per mole of feed. The molar
ratio of methane to C.sub.1+ organic oxygenate in the feed is in
the range of from 0.6:1 to 20:1 and the molar ratio of methane to
C.sub.2+ aliphatic hydrocarbon in the feed is in the range of from
0.1:1 to 20:1. The process includes contacting the feed with a
catalyst comprising at least one molecular sieve and at least one
dehydrogenation component under conditions, including a temperature
.ltoreq.700.degree. C., effective to convert at least part of the
methane, C.sub.2+ hydrocarbon, and C.sub.1+ organic oxygenate in
the feed to a product comprising at least 5 wt. % of C.sub.5+
hydrocarbon, based on the weight of the product. At least a portion
of the C.sub.5+ hydrocarbon can be separated from the product and
conducted away, e.g., for storage and/or further processing. The
methane can be derived from natural gas, for example. The C.sub.1+
organic oxygenate can be produced from syngas, with the syngas
being optionally derived from natural gas. The C.sub.2+ aliphatic
hydrocarbon can be derived from natural gas, e.g., from the same
natural gas from which the methane is derived. The natural gas can
be a wet natural gas, such as shale gas.
When the methane and C.sub.2+ aliphatic hydrocarbon are derived
from natural gas, aspects of the invention provide a convenient
method for natural gas upgrading. The closeness of atmospheric
boiling points among methane and C.sub.2+ aliphatic hydrocarbon in
the natural gas leads to complications in separating one or more of
these molecules, e.g., separating from the natural gas a portion of
the methane for use as a reactant or fuel. Utilizing the present
process for converting at least a portion of the C.sub.2+ aliphatic
hydrocarbon in the natural gas to C.sub.5+ hydrocarbon having a
significantly greater atmospheric boiling point considerably
simplifies this separation problem. Instead of a relatively
difficult methane separation from natural gas upstream of the
process, unconverted methane can be more easily separated from the
higher-boiling C.sub.5+ hydrocarbon in the product downstream of
the process. Reaction conditions can be adjusted to increase or
decrease the amount of unconverted methane available for separation
as desired.
It has also been found that utilizing an inorganic oxygenate in the
methane conversion increases the efficiency of the reaction,
obviating the need for a C.sub.2+ aliphatic hydrocarbon
co-reactant. It was believed that the formation of C.sub.5+
hydrocarbon from methane, and particularly the production of
aromatics from methane, would require an organic oxygenate
co-reactant to produce CH.sub.x fragments. It has surprisingly been
found that this is not the case. While not wishing to be bound by
any theory or model, it is believed that sufficient hydrogen is
made available to the reaction from the methane cracking, obviating
the need for an organic oxygenate as a source of CH.sub.x
fragments. In other words, it is believed that the chemistry is
different from the case where organic oxygenate is utilized as the
sole co-reactant. The inorganic oxygenate can be utilized in
combination with organic oxygenate, e.g., at an organic
oxygenate:inorganic oxygenate molar ratio in the range of 0.1 to
20, e.g., 2 to 10, such as 3 to 10. The inorganic oxygenate can be
utilized in combination with C.sub.2+ aliphatic hydrocarbon, e.g.,
at a C.sub.2+ aliphatic hydrocarbon:inorganic oxygenate molar ratio
in the range of 0.1 to 20, e.g., 2 to 10, such as 3 to 10. In
certain aspects, the inorganic oxygenate is utilized with both
organic oxygenate and C.sub.2+ aliphatic hydrocarbon.
These findings have led to the development of processes for
converting to C.sub.5+ hydrocarbon a feed comprising C.sub.1+
inorganic oxygenate and .gtoreq.9 mole % methane, the mole percent
being per mole of feed. The molar ratio of methane to C.sub.1+
inorganic oxygenate in the feed is in the range of from 0.6:1 to
20:1. The process includes contacting the feed with a catalyst
comprising at least one molecular sieve and at least one
dehydrogenation component under conditions, including a temperature
.ltoreq.700.degree. C., effective to convert at least part of the
methane and the C.sub.1+ inorganic oxygenate in the feed to a
product comprising at least 5 wt. % of C.sub.5+ hydrocarbon, based
on the weight of the product. At least a portion of the C.sub.5+
hydrocarbon can be separated from the product and conducted away,
e.g., for storage and/or further processing. Optionally, the feed
has a molar ratio of molecular hydrogen to C.sub.1+ inorganic
oxygenate in the range of from 0.5:1 to 20:1. The molecular
hydrogen and C.sub.1+ inorganic oxygenate can be derived from
syngas, for example. The methane can be derived for natural gas,
for example.
DETAILED DESCRIPTION
Definitions
For the purpose of this description and appended claims the
following terms are defined. The term "Cn" hydrocarbon wherein n is
a positive integer, e.g., 1, 2, 3, 4, or 5, means a hydrocarbon
having n number of carbon atom(s) per molecule. The term "Cn+"
hydrocarbon wherein n is a positive integer, e.g., 1, 2, 3, 4, or
5, as used herein, means a hydrocarbon having at least n number of
carbon atom(s) per molecule. The term "Cn-" hydrocarbon wherein n
is a positive integer, e.g., 1, 2, 3, 4, or 5, as used herein,
means a hydrocarbon having no more than n number of carbon atom(s)
per molecule. The term "aromatics" means hydrocarbon molecules
containing at least one aromatic core. The term "hydrocarbon"
encompasses mixtures of hydrocarbon, including those having
different values of n. The term "organic oxygenate" means molecules
having the formula CnH.sub.2n+1OCmH.sub.2m+1, wherein C, H and O
are carbon, hydrogen and oxygen, respectively; n is an integer
having a value .gtoreq.1, e.g., in the range of from 1 to 4; and m
is an integer having a value .gtoreq.zero, e.g., in the range of
from zero to 4. Examples of organic oxygenate include one or more
of methanol, ethanol, dimethyl ether, and diethyl ether. The term
"inorganic oxygenate" means oxygenate molecules that do not satisfy
the specified formula for organic oxygenate. A Cn oxygenate
molecule contains n carbon atoms, where n is an integer .gtoreq.1.
This term encompasses mixtures of carbon-containing oxygenate
molecules having different molecular weights and/or different
values of n. Examples of C.sub.1+ inorganic oxygenate include one
or more of aldehyde, carbon monoxide, and carbon dioxide. The term
"syngas" means a mixture comprising .gtoreq.12 mole % molecular
hydrogen and .gtoreq.0.4 mole % carbon monoxide, the mole percents
being per mole of the mixture.
As used herein, the numbering scheme for the groups of the Periodic
Table of the Elements is as disclosed in Chemical and Engineering
News, 63(5), 27 (1985).
The present disclosure relates to a process for the production of
C.sub.5+ hydrocarbon, particularly aromatics from feeds containing
methane. In certain aspects, the feed comprises methane, C.sub.1+
organic oxygenate, and C.sub.2+ aliphatic hydrocarbon, such as
C.sub.2+ alkane. In other aspects, the feed comprises methane,
C.sub.1+ inorganic oxygenate, and optionally (i) C.sub.2+ aliphatic
hydrocarbon and/or (ii) C.sub.1+ organic oxygenate. Representative
feeds will now be described in more detail. The invention is not
limited to these feeds, and this description is not meant to
foreclose other feeds within the broader scope of the
invention.
Feeds Comprising Methane, Organic Oxygenate, and C.sub.2+ Aliphatic
Hydrocarbon
In certain aspects, the feed comprises .gtoreq.9 mole % of methane,
e.g., .gtoreq.25 mole %, such .gtoreq.40 mole %; C.sub.1+ organic
oxygenate; and C.sub.2+ aliphatic hydrocarbon; wherein (i) the
molar ratio of methane to C.sub.1+ organic oxygenate in the feed is
in the range of from 0.6:1 to 20:1, such as from 4:1 to 10:1, for
example from 5:1 to 10:1; and (ii) the molar ratio of C.sub.2+
aliphatic hydrocarbon to C.sub.1+ organic oxygenate in the feed is
in the range of from 0.1:1 to 20:1 such as from 2:1 to 10:1, for
example from 3:1 to 10:1. The mole percents are based on per mole
of feed. Generally, at least a portion of the feed is in the vapor
phase during the conversion. For example, .gtoreq.75.0 wt. %, e.g.,
.gtoreq.90.0 wt. %, such as .gtoreq.99.0 wt. % of the feed can be
in the vapor phase during the conversion, the weight percents being
based on the weight of the feed. Examples of suitable feeds
comprise from 40 mole % to 80 mole % of methane, from 1 mole % to
15 mole % acetylene, and from 1 mole % to 40 mole % C.sub.2+
aliphatic hydrocarbon, the mole percents being per mole of feed.
The remainder of the feed, if any, can comprise diluent, for
example.
The methane can be obtained from natural gas, for example. Although
separate sources of methane and C.sub.2+ aliphatic hydrocarbon can
be utilized, one preferred source of these feed components is wet
natural gas, that is natural gas containing some or all of the
higher hydrocarbon, particularly C.sub.2 to C.sub.5 hydrocarbon,
co-produced with methane. A particularly preferred source of
natural gas is shale gas. In this way, the complex and costly
process of separating methane from the higher hydrocarbon present
in natural gas can be simplified and the natural gas can be
converted to easily transport liquid hydrocarbon.
In certain aspects, the C.sub.1+ organic oxygenate comprises a
compound represented by a general formula:
CnH.sub.2n.sub.+1OCmH.sub.2m.sub.+1, wherein C, H and O are carbon,
hydrogen and oxygen, respectively; n is an integer having a value
from 1 to 4, e.g., from 1 to 3, such as 1 or 2; and m is an integer
having a value from zero to 3, e.g., from zero to 2, such as zero
or 1. Examples of suitable C.sub.1+ organic oxygenate include
methanol, ethanol, dimethyl ether, diethyl ether, dipropyl ether,
dibutyl ether, methyl ethyl, ether, methyl propyl ethers, methyl
butyl ethers, and mixture thereof. Preferred C.sub.1+ organic
oxygenate includes methanol, ethanol, dimethyl ether, diethyl
ether, and mixtures thereof. In certain aspects, the C.sub.1+
organic oxygenate comprises .gtoreq.90.0 wt. % of C.sub.1 to
C.sub.4 alcohol and/or C.sub.2 to C.sub.8 dialkyl ether, based on
the weight of the C.sub.1+ organic oxygenate, e.g., .gtoreq.90.0
wt. % of methanol, ethanol, dimethyl ether, diethyl ether and
mixtures thereof.
In certain aspects, the organic oxygenate is methanol produced from
natural gas via syngas. The syngas can comprise, e.g., molecular
hydrogen and .gtoreq.5.0 wt. % of carbon monoxide, based on the
weight of the syngas, and the syngas can have an
H.sub.2:(CO+CO.sub.2) molar ratio in the range of from 0.5 to 20,
e.g., an H.sub.2:CO molar ratio in the range of from 0.5 to 20,
e.g., 0.6 to 4.
The syngas can be produced by any convenient method, including
conventional methods such as the partial oxidation of methane
and/or the steam reforming of methane. Suitable methods include
those described in U.S. Patent Application Publication Nos.
2007/0259972 A1, 2008/0033218 A1, and 2005/0107481, each of which
is incorporated by reference herein in its entirety.
Syngas can be produced, e.g., by contacting methane with steam in
the presence of a catalyst, such as one or more metals or compounds
thereof selected from Groups 7 to 10 of the Periodic Table of the
Elements supported on an attrition resistant refractory support,
such as alumina. The contacting is normally conducted at high
temperature, such as from 800.degree. C. to 1100.degree. C., and
pressures up to 5000 kPa such that the stream converts the methane
to carbon monoxide and hydrogen according to reactions, such as:
CH.sub.4+H.sub.2O=CO+3H.sub.2.
Steam reforming is energy intensive in that the process consumes
over 200 kJ/mole of methane consumed. A more preferred process of
producing syngas is therefore is partial oxidation, in which the
methane is burned in the presence of a catalyst and in an oxygen
lean environment to produce carbon monoxide and hydrogen, according
to the following representative reaction:
CH.sub.4+1/2O.sub.2.fwdarw.CO+2H.sub.2.
It will be appreciated that steam reforming produces syngas with a
molar ratio of H.sub.2:CO of about 3:1, whereas the product of the
partial oxidation of methane has a H.sub.2:CO of about 2:1. The
H.sub.2:CO molar ratio of the syngas is not critical and in fact
aspects of the invention utilizing syngas having an H.sub.2:CO
molar ratio <2.0, e.g., <1.5, or even <1.1.
In certain aspects, the syngas is catalytically converted to
organic C.sub.1+ oxygenate, e.g., C.sub.1+ alcohol, such as
methanol. The conversion of syngas to methanol can be carried out
at very high selectivity's using a mixture of copper, zinc oxide,
and alumina at a temperature of 200.degree. C. to 400.degree. C.
and pressures of 50-500 atm. In addition to Cu/ZnO/Al.sub.2O.sub.3,
other catalyst systems suitable for methanol synthesis include
Zn/VCr.sub.2O.sub.3, Cu/ZnO, Cu/ZnO/Cr.sub.2O.sub.3, Cu/ThO.sub.2,
CoS.sub.x, MoS.sub.x, Co--MoS.sub.x, Ni--S.sub.x, Ni--MoS.sub.x,
and Ni--Co--MoS.sub.x.
Besides methane and organic oxygenate, the feed can further
comprise C.sub.2+ aliphatic hydrocarbon. In certain aspects, the
C.sub.2+ aliphatic hydrocarbon comprises C.sub.2+ alkane, such as
C.sub.2 to C.sub.5 alkane. For example the C.sub.2+ aliphatic
hydrocarbon can comprise .gtoreq.50.0 wt. % of C.sub.2 to C.sub.5
alkane, based on the weight of the C.sub.2+ aliphatic hydrocarbon,
e.g., .gtoreq.75.0 wt. %, such as .gtoreq.90.0 wt. %, or
.gtoreq.99.0 wt. %. Another suitable source of methane and C.sub.2+
aliphatic hydrocarbon is product obtained from the oxidative
conversion of methane to ethylene and higher hydrocarbon ("OCM").
OCM is a process in which methane is reacted with an
oxygen-containing gas in the presence of a catalyst, such as an
alkaline earth/rare earth metal oxide catalyst, such as Sr-promoted
La.sub.2O.sub.3, at a temperature of 600.degree. C. to 800.degree.
C. and a pressure is 1 to 10 bars. The reaction is described in,
for example, U.S. Pat. No. 5,336,825, the entire contents of which
are incorporated herein by reference. The process couples the
methane into higher hydrocarbon, such as ethylene, by reactions
such as: 2CH.sub.4+O.sub.2.fwdarw.C.sub.2H.sub.42H.sub.2O.
In the process, methane is activated heterogeneously on the
catalyst surface, forming methyl free radicals, which then couple
in the gas phase to form ethane, which subsequently undergoes
dehydrogenation to form ethylene. The process is accompanied by the
non-selective reaction of methyl radicals and oxygen in the gas
phase to produce carbon monoxide and carbon dioxide. The product of
the OCM reaction is therefore a mixture comprising C.sub.2+
aliphatic hydrocarbon, water, CO, CO.sub.2 and residual oxygen and
methane. The methane and/or C.sub.2+ aliphatic hydrocarbon can be
separated from the OCM product and utilized as feed components with
the C.sub.1+ organic oxygenate.
This approach significantly lessens disadvantages encountered in
operating conventional OCM processes, in that the need to separate
C.sub.2/C.sub.3 olefins at low concentration from the OCM product
is avoided, while the C.sub.2/C.sub.3 olefins are converted to less
volatile C.sub.5+ hydrocarbon which can be more easily separated
from the methane. Other OCM by-products, such as residual oxygen,
CO and/or CO.sub.2 can be separated from the OCM product and
utilized as feed for one or more syngas processes, e.g., to produce
syngas utilized for synthesizing the C.sub.1+ organic
oxygenate.
Yet another suitable source of methane and C.sub.2+ aliphatic
hydrocarbon is the product of the non-catalytic pyrolysis of
methane in the presence of a limited oxygen environment to produce
C.sub.2+ aliphatic hydrocarbon such as ethylene and/or propylene.
Such a process is described in, for example, in International
Patent Publication No. WO 2012/099674A2, which is incorporated by
reference herein in its entirety. The product is a complex mixture
comprising C.sub.2+ aliphatic hydrocarbon (primarily ethylene,
propylene and higher hydrocarbon), water, CO, CO.sub.2 and residual
methane. The methane and/or desired C.sub.2+ aliphatic hydrocarbon
can be separated from the product and utilized as feed components
with the C.sub.1+ organic oxygenate.
Besides methane, organic oxygenate, and C.sub.2+ aliphatic
hydrocarbon, the feed can further comprise diluent. Optionally, the
feed further comprises .gtoreq.0.1 mole % diluent, based on per
mole feed. Diluent generally comprises species which do not react
in significant amounts with methane and/or organic oxygenate to
produce C.sub.5+ hydrocarbon under the specified operating
conditions. Suitable diluent includes one or more of molecular
hydrogen; hydrogen sulfide, and molecular nitrogen. In certain
aspects, the feed comprises diluent in an amount in the range of
from 0.1 mole % to 50 mole %, based on per mole of feed. Where
present, some or all of the diluent can be present as by-products
of the process used to produce the feed's methane and/or organic
oxygenate.
Feeds Comprising Methane and Inorganic Oxygenate
In certain aspects, the feed comprises C.sub.1+ inorganic
oxygenate, and .gtoreq.9 mole % of methane, e.g., .gtoreq.25 mole
%, such .gtoreq.40 mole %, wherein the molar ratio of methane to
C.sub.1+ inorganic oxygenate in the feed is in the range of from
0.6:1 to 20:1, such as from 5:1 to 15:1, for example from 7:1 to
10:1. The mole percents are based on per mole of feed. Generally,
at least a portion of the feed is in the vapor phase during the
conversion. For example, .gtoreq.75.0 wt. %, e.g., .gtoreq.90.0 wt.
%, such as .gtoreq.99.0 wt. % of the feed can be in the vapor phase
during the conversion, the weight percents being based on the
weight of the feed. Optionally, the feed further comprises
molecular hydrogen. The feed can have, e.g., a molecular
hydrogen:C.sub.1+ inorganic oxygenate molar ratio .gtoreq.0.6,
e.g., .gtoreq.1.0, such as .gtoreq.10.0. In certain aspects, the
feed has a molecular hydrogen:C.sub.1+ inorganic oxygenate molar
ratio in the range of from 0.5:1 to 20:1, e.g., 0.6:1 to 20:1.
Optionally, the methane is obtained from natural gas, e.g., wet
natural gas. The same natural gas sources can be utilized as
specified for feeds containing C.sub.1+ organic oxygenate.
The C.sub.1+ inorganic oxygenate can comprise, e.g., one or more of
CO, CO.sub.2 and formaldehyde. For example, the C.sub.1+ inorganic
oxygenate can comprise .gtoreq.50.0 wt. % of CO, based on the
weight of the C.sub.1+ inorganic oxygenate, such as .gtoreq.75.0
wt. %, or .gtoreq.90.0 wt. %, or .gtoreq.99.0 wt. %. Optionally,
balance of C.sub.1+ inorganic oxygenate, if any, can be CO.sub.2.
The feed can have, e.g., a molecular hydrogen:(CO+CO.sub.2) molar
ratio .gtoreq.0.6, e.g., .gtoreq.1.0, such as .gtoreq.10.0, or in
the range of from about 0.6 to about 20. In certain aspects, the
C.sub.1+ inorganic oxygenate is substantially all CO. The feed can
have, e.g., a molecular hydrogen:CO molar ratio .gtoreq.0.6, e.g.,
.gtoreq.1.0, such as .gtoreq.10.0, or in the range of from about
0.6 to about 20. Optionally, the molecular hydrogen:CO molar ratio
is .gtoreq.4, such as in the range of from 1 to 4.
In certain aspects, (i) the C.sub.1+ inorganic oxygenate comprises
CO and (ii) the CO is obtained from syngas. The syngas can
comprise, e.g., molecular hydrogen and .gtoreq.5.0 wt. % of carbon
monoxide, based on the weight of the syngas. The syngas can have an
H.sub.2:(CO+CO.sub.2) molar ratio in the range of from 0.5 to 20,
e.g., in the range of from 0.6 to 4, such as an H.sub.2:CO molar
ratio in the range of from 0.6 to 4. The syngas can be produced by
any convenient method, including conventional methods such as those
specified in connection with feeds containing C.sub.1+ organic
oxygenate. As in the case of those feeds, methane for syngas
generation can be obtained, e.g., from natural gas.
Another suitable source of methane, C1+ inorganic oxygenate and C2+
aliphatic hydrocarbon is OCM product. Since OCM product comprises
unconverted methane, C.sub.2+ aliphatic hydrocarbon, and C.sub.1+
inorganic oxygenate (primarily CO and CO.sub.2), the OCM product
can be utilized directly as a feed for the instant process for
converting methane to C.sub.5+ hydrocarbon such as aromatics,
utilizing the specified catalyst. The OCM product alone can be fed
to the specified conversion step or can be combined with additional
methane, C.sub.1+ inorganic oxygenates, molecular hydrogen, and/or
C.sub.2+ hydrocarbon. Similarly the product of the non-catalytic
pyrolysis of methane, as specified for feeds containing C.sub.1+
organic oxygenates, can be conducted to the specified conversion
reaction for producing the C.sub.5+ hydrocarbon. The pyrolysis
product alone can be fed to the specified conversion step or can be
combined with additional methane, C.sub.1+ inorganic oxygenate,
molecular hydrogen, and/or C.sub.2+ hydrocarbon.
Optionally, the feed further comprises .gtoreq.0.1 mole % diluent,
based on per mole of feed. Diluent generally comprises species
which do not react in significant amounts with methane and/or
C.sub.1+ inorganic oxygenate to produce C.sub.5+ hydrocarbon under
the specified operating conditions. Suitable diluent includes one
or more of molecular hydrogen, hydrogen sulfide, and molecular
nitrogen. In certain aspects, the feed comprises diluent in an
amount in the range of from 0.1 mole % to 50 mole %, based on per
mole of feed. Where present, some or all of the diluent can be
present as by-products of the process used to produce the feed's
methane and/or C.sub.1+ inorganic oxygenate.
Converting the Feed to C.sub.5+ Hydrocarbon
In certain aspects, the invention relates to processes which
include contacting the feed with a bi-functional catalyst
comprising at least one molecular sieve and at least one
dehydrogenation component to produce a product comprising
.gtoreq.5.0 wt. % of aromatics based on the weight of the product.
The process can be carried out over a broad range of
methane:oxygenate molar ratio, and can be carried out efficiently
at a temperature that is significantly below that utilized in prior
art processes. Although the mechanisms of the reactions occurring
in the present process are not fully understood, it is believed
that the methane is activated by the C.sub.1+ oxygenate at the
metal and acid sites of the bi-functional catalyst allowing the
methane and, where present, the C.sub.2+ aliphatic hydrocarbon, to
be aromatized at temperatures below 700.degree. C., e.g., at a
temperature .ltoreq.300.degree. C. Whereas the non-oxidative
aromatization of methane is thermodynamically restrained at low
temperatures and the aromatization of C.sub.1+ oxygenates is highly
exothermic, the present process couples the simultaneous
endothermic conversion of methane and the exothermic aromatization
of the C.sub.1+ oxygenate, rendering the process highly energy
efficient. The process can utilize one or more catalysts, e.g., at
least one bi-functional catalyst. Representative bi-functional
catalysts contain at least one acidic functionality (generally
provided by the molecular sieve component) and at least one
dehydrogenation functionality (generally provided by the
dehydrogenation metal component). Certain catalysts useful in the
invention will now be described in more detail. The invention is
not limited to these catalysts, and this description is not meant
to foreclose other catalysts within the broader scope of the
invention.
In certain aspects, the catalyst comprises at least one medium pore
size molecular sieve having a Constraint Index of 2-12 (as defined
in U.S. Pat. No. 4,016,218). Examples of such medium pore molecular
sieves include ZSM-5, ZSM-11, ZSM-12, ZSM-22, ZSM-23, ZSM-35,
ZSM-48 and mixtures and intermediates thereof. ZSM-5 is described
in detail in U.S. Pat. No. 3,702,886 and Re. 29,948. ZSM-11 is
described in detail in U.S. Pat. No. 3,709,979. A ZSM-5/ZSM-11
intermediate structure is described in U.S. Pat. No. 4,229,424.
ZSM-12 is described in U.S. Pat. No. 3,832,449. ZSM-22 is described
in U.S. Pat. No. 4,556,477. ZSM-23 is described in U.S. Pat. No.
4,076,842. ZSM-35 is described in U.S. Pat. No. 4,016,245. ZSM-48
is more particularly described in U.S. Pat. No. 4,234,231.
Optionally, the molecular sieve is one comprising at least one set
of pores of substantially uniform size extending through the
molecular sieve, wherein geometric mean of the cross-sectional
dimensions of each of the pores is >5 .ANG., or >5.3 .ANG.,
e.g., .gtoreq.5.4 .ANG. such as .gtoreq.5.5 .ANG., or in the range
of 5 .ANG. to 7 .ANG., or 5.4 .ANG. to 7 .ANG..
In other aspects, the catalyst employed in the present process
comprises at least one molecular sieve of the MCM-22 family. As
used herein, the term "molecular sieve of the MCM-22 family" (or
"material of the MCM-22 family" or "MCM-22 family material" or
"MCM-22 family zeolite") includes one or more of: (i) molecular
sieves made from a common first degree crystalline building block
unit cell, which unit cell has the MWW framework topology. (A unit
cell is a spatial arrangement of atoms which if tiled in
three-dimensional space describes the crystal structure. Such
crystal structures are discussed in the "Atlas of Zeolite Framework
Types", Fifth edition, 2001, the entire content of which is
incorporated as reference; (ii) molecular sieves made from a common
second degree building block, being a 2-dimensional tiling of such
MWW framework topology unit cells, forming a monolayer of one unit
cell thickness, preferably one c-unit cell thickness; (iii)
molecular sieves made from common second degree building blocks,
being layers of one or more than one unit cell thickness, wherein
the layer of more than one unit cell thickness is made from
stacking, packing, or binding at least two monolayers of one unit
cell thickness. The stacking of such second degree building blocks
can be in a regular fashion, an irregular fashion, a random
fashion, or any combination thereof; and (iv) molecular sieves made
by any regular or random 2-dimensional or 3-dimensional combination
of unit cells having the MWW framework topology.
Molecular sieves of the MCM-22 family include those molecular
sieves having an X-ray diffraction pattern including d-spacing
maxima at 12.4.+-.0.25, 6.9.+-.0.15, 3.57.+-.0.07 and 3.42.+-.0.07
Angstrom. The X-ray diffraction data used to characterize the
material are obtained by standard techniques using the K-alpha
doublet of copper as incident radiation and a diffractometer
equipped with a scintillation counter and associated computer as
the collection system.
Materials of the MCM-22 family include MCM-22 (described in U.S.
Pat. No. 4,954,325), PSH-3 (described in U.S. Pat. No. 4,439,409),
SSZ-25 (described in U.S. Pat. No. 4,826,667), ERB-1 (described in
European Patent No. 0293032), ITQ-1 (described in U.S. Pat. No.
6,077,498), ITQ-2 (described in International Patent Publication
No. WO 97/17290), MCM-36 (described in U.S. Pat. No. 5,250,277),
MCM-49 (described in U.S. Pat. No. 5,236,575), MCM-56 (described in
U.S. Pat. No. 5,362,697), and mixtures thereof. Related zeolite
UZM-8 is also suitable for use as a molecular sieve component of
the present catalyst.
In certain aspects, the molecular sieve employed in the present
process may be an aluminosilicate or a substituted aluminosilicate
in which part of all of the aluminum is replaced by a different
trivalent metal, such as gallium or indium.
The invention can be practiced using catalysts that have been
subjected to one or more catalyst treatments, e.g., selectivation.
For example, the catalyst can comprise at least one molecular sieve
which has been selectivated, either before introduction of the
catalyst into the reactor or in-situ in the reactor, by contacting
the catalyst with a selectivating agent, such as at least one
organosilicon in a liquid carrier and subsequently calcining the
catalyst at a temperature of 350.degree. C. to 550.degree. C. This
selectivation procedure can be repeated two or more times and
alters the diffusion characteristics of the catalyst such that the
formation of para-xylene over other xylene isomers is favored. Such
a selectivation process is described in detail in U.S. Pat. Nos.
5,633,417 and 5,675,047, the entire contents of which are
incorporated herein by reference.
In addition to the molecular sieve component, the catalyst
generally comprises at least one dehydrogenation component, e.g.,
at least one dehydrogenation metal. The dehydrogenation component
is typically present in an amount of at least 0.1 wt. %, such as
from 0.1 to 5 wt. %, of the overall catalyst. The dehydrogenation
component can comprise one or more neutral metals selected from
Groups 3 to 13 of the Periodic Table of the Elements, such as Ga,
In, Zn, Cu, Re, Mo, W, La, Fe, Ag, Pt, Pd, and/or one or more
oxides, sulfides and/or carbides of these metals. The
dehydrogenation component can be provided on the catalyst in any
manner, for example by conventional methods such as impregnation or
ion exchange of the molecular sieve with a solution of a compound
of the relevant metal, followed by conversion of the metal compound
to the desired form, namely neutral metal, oxide, sulfide and/or
carbide. Part or all of the dehydrogenation metal may also be
present in the crystalline framework of the molecular sieve. A
carbonyl conversion functionality can also be used when the
co-reactant comprises inorganic oxygenate, e.g., one or more of Cu,
Co, Cr, Fe, Mo, Zn, such as in one or more of metal, oxide,
sulfide, etc.
In one aspect, the bi-functional catalyst used in the present
process is selected from the group consisting of Ga and/or
In-modified ZSM-5 type zeolites such as Ga and/or In-impregnated
H-ZSM-5, Ga and/or In-exchanged H-ZSM-5, H-gallosilicate of ZSM-5
type structure and H-galloaluminosilicate of ZSM-5 type structure.
These zeolites can also be prepared by any suitable method,
including conventional methods.
For example, the bi-functional catalyst may contain tetrahedral
aluminum and/or gallium, which is present in the zeolite framework
or lattice, and octahedral gallium or indium, which is not present
in the zeolite framework but present in the zeolite channels in
close vicinity to the zeolitic protonic acid sites, and which is
attributed to the presence of tetrahedral aluminum and gallium in
the catalyst. The tetrahedral or framework Al and/or, Ga is
responsible for the acid function of the catalyst and octahedral or
non-framework Ga and/or In is responsible for the dehydrogenation
function of the catalyst. In one preferred aspect, the
bi-functional catalyst comprises H-galloaluminosilicate of ZSM-5
type structure having framework (tetrahedral) Si/Al and Si/Ga mole
ratios of about 10:1 to 100:1 and 15:1 to 150:1, respectively, and
non-framework (octahedral) Ga of about 0.5 to 0 wt. %.
In addition to the molecular sieve components and dehydrogenation
component, the catalyst may be composited with another material
which is resistant to the temperatures and other conditions
employed in the conversion reaction. Such materials include active
and inactive materials and synthetic or naturally occurring
zeolites as well as inorganic materials such as clays and/or oxides
such as alumina, silica, silica-alumina, zirconia, titania,
magnesia or mixtures of these and other oxides. The latter may be
either naturally occurring or in the form of gelatinous
precipitates or gels including mixtures of silica and metal oxides.
Clays may also be included with the oxide type binders to modify
the mechanical properties of the catalyst or to assist in its
manufacture. Use of a material in conjunction with the molecular
sieve, i.e., combined therewith or present during its synthesis,
which itself is catalytically active may change the conversion
and/or selectivity of the catalyst. Inactive materials suitably
serve as diluents to control the amount of conversion so that
products may be obtained economically and orderly without employing
other means for controlling the rate of reaction. These materials
may be incorporated into naturally occurring clays, e.g., bentonite
and kaolin, to improve the crush strength of the catalyst under
commercial operating conditions and function as binders or matrices
for the catalyst. The relative proportions of molecular sieve and
inorganic oxide matrix vary widely, with the sieve content ranging
from about 1 to about 90 percent by weight and more usually,
particularly, when the composite is prepared in the form of beads,
in the range of about 2 to about 80 weight percent of the
composite.
Process Conditions
In certain aspects, the invention relates to processes which
include contacting the feed with one or more of the specified
bi-functional catalysts, e.g., those comprising at least one
molecular sieve and at least one dehydrogenation component, to
produce a product comprising .gtoreq.5.0 wt. % of aromatics based
on the weight of the product. Selected process conditions for the
conversion will now be described in more detail. The invention is
not limited to these process conditions, and this description is
not meant to foreclose other process conditions within the broader
scope of the invention.
In certain aspects, conversion of the feed comprising methane and
co-reactants to aromatic hydrocarbon is generally conducted at a
temperature less than 700.degree. C., such as from 250.degree. C.
to 699.degree. C. and a pressure in the range of from 1 bar
(absolute) to 5 bar (absolute) (100 to 500 kPa absolute). Space
velocity is not critical, and the conversion conditions can
include, e.g., a gas hourly space velocity a feed gas hourly space
velocity of .gtoreq.100 cm.sup.3/h/g of catalyst. The conversion
process can be conducted in one or more fixed bed, moving bed or
fluidized bed reaction zones. The conversion can be operated, e.g.,
continuously, semi-continuously, or in batch mode.
In certain aspects, the conversion conditions include exposing the
specified feed in the presence of at least one specified catalyst
to a temperature in the range of from 275.degree. C. to 650.degree.
C., e.g., 300.degree. C. to 600.degree. C., such as 325.degree. C.
to 550.degree. C. The conversion conditions can further include a
pressure in the range of from 1.2 bar (abs) to 4 bar (abs), and a
feed gas hourly space velocity in the range of 100 cm.sup.3/h/g of
catalyst to 10,000 cm.sup.3/h/g of catalyst, e.g., 500 cm.sup.3/h/g
of catalyst to 5000 cm.sup.3/h/g of catalyst.
When operated utilizing the specified feed, in the presence of at
least one of the specified catalysts, and with the specified
conversion conditions, the products of the conversion are mainly
C.sub.5+ hydrocarbon, water, and lesser amounts of ethylene,
ethane, propylene, propane and C.sub.4 hydrocarbon. For example,
the product of the conversion can comprise, e.g., (i) .gtoreq.5.0
wt. % of C.sub.5+ hydrocarbon, e.g., .gtoreq.10.0 wt. %, such as
.gtoreq.15 wt. %; (ii) and .ltoreq.10.0 wt. % C.sub.2 to C.sub.4
hydrocarbon, e.g., 5.0 wt. %, such as .gtoreq.1.0 wt. %; the weight
percents being based on the weight of the product. Methane
conversion is generally .gtoreq.5.0 wt. %, based on the weight of
methane in the feed, e.g., .gtoreq.10.0 wt. %, such as .gtoreq.15.0
wt. %. The C.sub.5+ hydrocarbon comprises mainly aromatics, e.g.,
.gtoreq.50.0 wt. % of C.sub.6 to C.sub.10 aromatics, based on the
weight of the product's C.sub.5+ hydrocarbon, such as .gtoreq.75.0
wt. %, or .gtoreq.90.0 wt. %, or .gtoreq.95.0 wt. %. For example,
the molar ratio of aromatic hydrocarbon produced to methane
converted is generally .gtoreq.3.5:1, such as .gtoreq.4:1.
The C.sub.6 to C.sub.10 aromatics can readily be removed from the
product by any convenient method, e.g., by one or more conventional
fractionation and extraction techniques.
All patents, test procedures, and other documents cited herein,
including priority documents, are fully incorporated by reference
to the extent such disclosure is not inconsistent and for all
jurisdictions in which such incorporation is permitted.
While the illustrative forms disclosed herein have been described
with particularity, it will be understood that various other
modifications will be apparent to and can be readily made by those
skilled in the art without departing from the spirit and scope of
the disclosure. Accordingly, it is not intended that the scope of
the claims appended hereto be limited to the examples and
descriptions set forth herein but rather that the claims be
construed as encompassing all the features of patentable novelty
which reside herein, including all features which would be treated
as equivalents thereof by those skilled in the art to which this
disclosure pertains.
When numerical lower limits and numerical upper limits are listed
herein, ranges from any lower limit to any upper limit are
contemplated, and are expressly within the scope of the invention.
The term "comprising" is synonymous with the term "including".
Likewise whenever a composition, an element or a group of
components is preceded with the transitional phrase "comprising",
it is understood that we also contemplate the same composition or
group of components with transitional phrases "consisting
essentially of," "consisting of", "selected from the group of
consisting of," or "is" preceding the recitation of the
composition, component, or components, and vice versa.
* * * * *